Case 1: A chain says “from a man,” with no reliable second route identifying him: the intermediary is mubham.
Case 2: “ʿUmar ibn Khālid” is named, only one pupil reports from him, and no adequate endorsement exists: the basic case of majhūl al-ʿayn.
Case 3: The same one-pupil situation, but a qualified critic supplies credible authentication: the sole-pupil fact by itself no longer warrants treating the man as unknown.
Case 4: Two pupils transmit from “Saʿīd ibn Sālim,” but reliable authentication is lacking: the issue is majhūl al-ḥāl / mastūr.
These are hypothetical names for classification only, not critical judgments on actual historical persons. Overall hadith grading still requires checking the remaining conditions.